Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 10,438	$ 11,998
Short-term investments	7,355	9,825
Accounts receivable	79	165
Unbilled revenue		3
Inventories — current	187	181
Prepaid expenses and other current assets	506	704
Total current assets	18,565	22,876
Property and equipment, net	460	395
Right of use asset	2,193
Inventories — noncurrent	701	746
Other noncurrent assets	31	7
Total assets	21,950	24,024
Current liabilities:
Accounts payable and accrued expenses	2,062	2,645
Amounts due to related parties	12	29
Unearned revenue — current	56	96
Operating lease liability — current	574
Other current liabilities	264	284
Total current liabilities	2,968	3,054
Operating lease liability — noncurrent	1,771
Common stock warrant liabilities	13,578	5,083
Other noncurrent liabilities	3,000	3,072
Total liabilities	21,317	11,209
Stockholders’ equity:
Common stock, $0.001 par value—150,000,000 shares authorized as of March 31, 2019 and December 31, 2018; 4,777,419 and 4,774,919 shares issued and outstanding as of March 31, 2019 and December 31, 2018, respectively	45	45
Additional paid-in capital	191,566	191,136
Accumulated deficit	(190,978)	(178,366)
Total stockholders’ equity	633	12,815
Total liabilities and stockholders’ equity	$ 21,950	$ 24,024